Attrition



Oct. 22, 1968 Filed March 2, 1965 C. R. LYON ATTRITION 6 Sheets-Sheet l .IIIIHHHH Il- .MMHHHII' Oct. 22, 1968 c. R; LYON 3,406,916

ATTR ITION Filed March 2, 1965 6 Sheets-Sheet 2 Oct. 22, 1968 c. R. LYON 3,406,916

ATTRITION Filed March 2, 1965 6 Sheets-Sheet 5 Oct. 22, 1968 c. R. LYON 3,406,916

ATTRITION Filed March 2, 1965 6 Sheets-Sheet 4 TIL a4.

Oct. 22, 1968 c. R. LYON 3,406,916

ATTRITION Filed March 2, 1965 I 6 Sheets-Sheet 5 Oct. 22, 1968 c. R. LYON 3, 1

ATTRITION Filed March 2, 1965 6 Sheets-Sheet 6 United States Patent 3,406,916 ATTRITION Charles R. Lyon, Fort Mill, S.C., assignor to Celanese Corporation, a corporation of Delaware Filed Mar. 2, 1965, Ser. No. 436,579 3 Claims. (Cl. 241-28) This invention relates to the attrition of woodpulp for use in the production of cellulose derivatives.

In the manufacture of cellulose derivatives it is customary to employ, as one of the starting materials, fibers of bleached woodpulp of high alpha cellulose content (socalled chemical pulp). The pulp is supplied, by the pulp manufacturer, in the form of sheet material prepared by drying a wet mass of the individual fibers. Before this pulp is converted chemically to the desired cellulose derivative (e.g. to an ester such as cellulose acetate) it is common practice to pass the sheet material to an attrition mill to separate the individual cellulose fibers, which may for example be on the order of 43- 4 inch in length. One conventional attrition mill used for this purpose employs two concentric disks, one of which is rotating at high speed relative to the other, which is usually stationary. The disks have opposing teeth which project into the attrition zone, between the disks, and which engage the dry pulp material as it passes through this zone. The stationary disk has a central hole through which the pulp sheet material is fed to the attrition zone, while the rotating disk is provided with knife elements facing this central hole and arranged in a more or less random pattern; these knife elements serve to cut the pulp material into smaller pieces which are thrown outward centrifugally through the space between the two disks. The resulting individual fibers which pass out from the periphery of the disks are taken up bya current of air, produced by the action of a suction fan, and delivered to a storage zone for conversion into the desired cellulose derivative.

The pulp sheet material, as furnished by the supplier, generally has a width of about 2 to 3 feet and a thickness of about A; inch, and is supplied in roll form or in large individual sheets. The feed hole in the stationary disk of the attrition mill is, for example, about 18 inches in diameter. In feeding the sheet material to the attrition mill, it has for many years been the practice for an operator to bend the edges of the sheet material upwardly, pass the material into the larger end of a conical chute leading to the intake opening of the attrition mill, and thereby urge the resulting folded or partially rolled sheet against the knife elements of the rotating disk.

It is an object of this invention to increase the rate of the production of pulp fibers in the attrition mill.

Another object of this invention is to improve the operation of the attrition mills used for the production of pulp fibers.

Other objects of this invention will be apparent from the following detailed description and claims. In this description and claims, all proportions are by weight unless otherwise indicated.

A device for use in one aspect of this invention is illustrated in the accompanying drawing in which:

FIGURE 1 is a side view showing the attrition mill coupled to a device for supplying the pulp material thereto;

FIGURE 2 is a view taken from the right end of FIG. 1;

FIGURE 3 is a view of the right end of FIG. 1 with portions in cross-section;

FIGURE 4 is a view of the right end of FIG. 1 showing the opposite side of the pulp-supplying device;

FIGURE 5 is a view taken from the same end as in FIG. 2 and showing portions in cross-section;

FIGURE 6 is a cross-sectional view of the pulp-supplying device showing details of the construction; and

3,406,916 Patented Oct. 22, 1968 FIGURE 7 is a perspective view of details of hammer elements and sheet-supporting elements.

In the drawing reference numeral 11 (FIG. 1) designates an attrition mill of conventional type (Sprout, Waldron) having a casing 12 and a pair of opposed toothed disks 13 and 14 (FIG. 3), the stationary disk 13 having a central opening 16 and the driven rotating disk 14 having cutter knife elements 17; the disk 14 is driven by a motor 18, whose drive shaft 18a is supported on bearings 18b (FIG. 1).

In the embodiment of the invention illustrated in the drawing there is mounted, in position to feed cellulose pulp material 19 (as from a roll 19a, FIG. 1) to the inlet opening 16, a combined hammer mill and conveying device, indicated generally as 21, comprising a hammer mill portion 22 (FIGS. 3 and 4) mounted on a vertical plate 23 arising from a base 24, which base also supports a conveyor portion 26 located just below the hammer mill portion 22.

At the inlet end of the hammer mill portion 22, there is mounted a pair of feed rolls 28, 29 (FIGS. 3 and 4) of sulficient length to accommodate the full width of the woodpulp sheet material, the lower feed roll 28 being suitably driven, as through a belt 31 fitted over a pulley 32 and driven by an electric motor 33 which may be mounted on the base 24. The upper feed roll 29, which is an idler roll, is biased downward, in any suitable fashion, as by a spring or weight (not shown) to press the sheet material, fed to the nip of these two rolls, against the driven roll 28. Advantageously, the rolls 28 are rubbercovered rolls.

Within the hammer mill portion 22 a series of spaced parallel hammers 36 are mounted on, and keyed to, a rotatable hammer shaft 37 which is driven in any suitable fashion, as by an electric motor 38 supported atop the hammer mill portion and connected to the hammer shaft 37 through a belt 39 engaging a pulley at the end of that shaft. The hammers 36 have central bearing areas 41 (FIG. 5) projecting on both sides of each hammer to provide for their rigid support and to act as spacers.

The hammers 36 are adapted to coact, in interfitting relation, with a set of spaced stationary cutter teeth 42 mounted on a stationary bar 43 and so positioned that the pulp sheet material, as it passes from the feed rolls, is supported on the cutter teeth and is struck and penetrated by the downwardly moving hammers, which then pass between the cutter teeth.

The hammers 36 in the embodiment illustrated in the drawing, are tapered, being of parallelogram shape, with two of the edges of the parallelogram disposed at about 45 to the other two edges to form sharp corners and are so mounted that, on rotation of the hammer shaft 37, their long flat edges strike the top of the pulp sheet material. The tapered construction of the hammers provides adequate strength while limiting the masses of the hammers at their outer edges, thus facilitating high speed rotation of the hammer shaft. Adjacent hammers, although in parallel planes, are mounted at an angle to each other; as shown in the drawing this angle is so that alternate hammers are parallel to each other. In one preferred embodiment the hammers 36 and the teeth 42 are uniformly spaced and are each about /2 inch wide, with straight flat vertical sides, and the hammer-tooth clearance, on each side of each hammer, is about /1 inch.

The action of the hammers 36 which may be rotated at, for example, 1800 rpm. with a tip velocity of 4500 feet per minute, breaks the sheet material into more or less rectangular chips or pieces, e.g. inch squares or /2 x 1 rectangles, depending on the relative preset, constant speeds of hammer rotation and of sheet feeding. For best results the sheet material being fed is struck by the opa erative ends of each hammer no later than it is struck by that portion of the hammer which is closer to the center of rotation of the hammer; in this way the pieces of pulp are chipped off from the forward end of the advancing sheet without cutting the sheet material into ribbons.

The chips of sheet material fall between the cutter teeth 42 through the large open top of a tapered conveyor housing 46 having a circular bottom 47 in which there is mounted a rotatable helical feed screw 48 whose axis is concentric with that of the center of curvature of the circular bottom 47. The screw 48 is suitably driven, as by an electric motor 51 mounted on the base 24 connected to the center shaft 52 of the feed screw 48 by means of a belt. The chips are delivered, by the action of the feed screw 48, directly to the inlet 16 of the attrition mill 11, which inlet is concentric with the feed screw 48.

It is found that the use of the arrangement described above makes it possible to triple the maximum practical continuous rate of feed of the sheet material to the attrition mill, without changing the speed of operation of the attrition mill, and with the use of substantially less power in the mill. The load on the attrition mill is found to be much more uniform, the mill operates with little, if any, of the bumping and grinding observed with the previous method, and maintenance costs are considerably reduced. Also, this invention eliminates the difficulties resulting from breaking of the cutter elements of the rotating disk and the need to sharpen these elements often. The usual frequent interruptions of operation due to breaking or tearing of the relatively weak pulp sheet material as it was fed to the attrition mill are also avoided.

In addition the use of this invention has been found to improve the properties (e.g. filtration characteristics) of cellulose acetate spinning solutions produced in conventional manner from the pulp, despite the tripled rate of operation. This effect is observed, for example, in solutions made, in the conventional manner, by acetylating the pulp fibers, ripening the acetylated product to produce secondary cellulose acetate and dissolving this cellulose acetate in acetone to form a viscous spinning solution, or dope," for use in the formation of continuous filaments.

It is to be understood that the foregoing detailed description is given merely by way of illustration, and that variations may be made therein without departing from the spirit of my invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for separating the fibers of a pulp sheet material by the action of an attrition mill, the improvement which comprises:

(a) feeding a pulp sheet to a chipping zone;

(b) supporting the sheet material in said zone at a plurality of spaced points along the leading edge thereof and for some distance back from the leading edge thereby forming a band of support for the sheet material, said support band having a leading edge and a back edge;

(c) striking the sheet material in spaces between said plurality of support points along the leading edge thereof while simultaneously striking it at the back edge of the support band whereby chips of pulp are chipped otf the pulp sheet.

2. Process as set forth in claim 1 in which said sheet has a thickness of about /8 inch, is positively fed to said zone, and the resulting chips fall between said spaced supporting points to a conveying zone where they are continuously transferred to the inlet of said attrition mill.

3. A process as set forth in claim 2 in which said striking is done at such a rate, in relation to the rate of feed of said sheet material that said sheet material is broken into rectangular chips about /2 to 1 inch in length.

References Cited UNITED STATES PATENTS 1,181,967 5/1916 Curtis 241-157 X 1,623,676 4/1927 Haug 241-157 X 1,774,309 8/1930 Anderson 241-18 X 1,795,603 3/1931 Hussey 24128 X 1,897,620 2/1933 Respess 24129 2,300,458 11/ 1942 Mazzucchelli.

WILLIAM W. DYER, 111., Primary Examiner.

HARRY F. PEPPER, JR., Examiner.

W. D. BRAY, Assistant Examiner. 

1. IN A PROCESS FOR SEPARATING THE FIBERS OF A PULP SHEET MATERIAL BY THE ACTION OF AN ATTRITION MILL, THE IMPROVEMENT WHICH COMPRISES: (A) FEEDING A PULP SHEET TO A CHIPPING ZONE; (B) SUPPORTING THE SHEET MATERIAL IN SAID ZONE AT A PLURALITY OF SPACED POINTS ALONG THE LEADING EDGE THEREOF AND FOR SOME DISTANCE BACK FROM THE LEADING EDGE THEREBY FORMING A BAND OF SUPPORT FOR THE SHEET MATERIAL, SAID SUPPORT BAND HAVING A LEADING EDGE AND A BACK EDGE; (C) STRIKING THE SHEET MATERIAL IN SPACES BETWEEN SAID PLURALITY OF SUPPORT POINTS ALONG THE LEADING EDGE THEREOF WHILE SIMULTANEOUSLY STRIKING IT AT THE BACK EDGE OF THE SUPPORT BAND WHEREBY CHIPS OF PULP ARE CHIPPED OFF THE PULP SHEET. 